Ionospheres of outer planets

Abstract

Ionospheres of Jupiter, Saturn and Uranus are reviewed on the basis of existing experimental measurements and theoretical models. The radio science experiments on Pioneer 10 and 11 and Voyager 1 and 2 indicate the presence of equatorial anomaly in the ionospheres of Jupiter and Saturn. Peak electron densities inferred by interpreting electrostatic discharges as lightning associated radio bursts, indicate large diurnal changes in the ionospheres of Saturn and Uranus. Simple photochemical models cannot explain the altitude of peak electron density in case of Jupiter and the peak electron density, as well as its altitude in case of Saturn. Factors like ion drifts, H2 vibrational temperatures, particle precipitation, water from the rings can play major role in the ionospheres of these planets. It appears that while the ionosphere of Jupiter is controlled by particle precipitation processes, the ionosphere of Saturn is influenced by water from the rings. For Uranian ionosphere, particle precipitation as well as water from the rings, are likely to be important.